1. Technical Field
The present invention generally relates to pneumatic tires and, more particularly, to a pneumatic tire having a body cord insert that improves the rolling resistance of the tire. Specifically, the present invention is directed to a pneumatic tire having a body cord divided into upper and lower sections wherein the ratio of the modulus of the upper section to the modulus of the lower section is reduced in order to decrease the rolling resistance of the tire. The ratio is reduced by providing a body cord insert around the bead assembly that increases the modulus of the lower section of the body cord.
2. Background Information
In an inflated and loaded condition, a radial tire is subject to bending moments at the shoulder areas in both the leading and trailing positions of the tire footprint. The strains and stresses created by the moments are directly related to the rolling resistance of the tire. The art recognizes that tire carcass design influences the rolling resistance of the tire and desires a tire carcass design that reduces the rolling resistance of the tire.
Previous research and studies have found that the body cord tension ratio (BCTR) strongly influences the rolling resistance of the tire. The BCTR includes the BCTR in the bead and shoulder portions of the tire. In general, the art recognizes that the rolling resistance is lower when the BCTR in the bead area is high. The art thus desires a tire carcass structure that increases the BCTR in the bead portion of the tire.
In view of the foregoing, an aspect of the present invention is to reduce the rolling resistance of a pneumatic tire by improving the carcass design. In particular, the invention improves the rolling resistance by optimizing the body cord stiffness. The invention optimizes body cord stiffness by dividing the body cord in a tire section into two sections and optimizing the ratio of stiffnesses of the areas to reduce rolling resistance. The invention provides a tire carcass having a body cord insert disposed around the bead assembly to increase the BCTR in the bead area. The body cord insert is disposed below the maximum section width and includes two end portions that are disposed against each other above the bead filler. In one embodiment, the ends of the body cord insert are disposed 0.3 inches to 0.6 inches from each other. The upper end portion of the body cord turn up is disposed zero to 0.5 inches below the maximum section width of the tire.